chore(telegraf): Prepare for data formats (serializers) documentation generated from upstream (influxdata/telegraf).

- Moves data_format and subdirs to `content/telegraf/v1/{input,output}-data-formats
- Adds _index.md with metadata similar to {input,output}-plugins files.
- Included shortcode reference, but haven't made any shortcode updates yet.

content/telegraf/v1/input-data-formats/_index.md

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+---
+title: Telegraf input data formats
+list_title: Input data formats
+description: Telegraf supports parsing input data formats into Telegraf metrics.
+menu:
+  telegraf_v1_ref:
+    name: Input data formats
+    parent: data_formats_reference
+    identifier: input_data_formats_reference
+    weight: 20
+tags: [input-data-formats, input-serializers]
+---
+
+Telegraf supports the following input data formats for parsing data into [metrics](/telegraf/v1/metrics/).
+Input plugins that support these formats include a `data_format` configuration option.
+
+For example, in the [Exec input plugin](/telegraf/v1/input-plugins/exec/):
+
+```toml
+[[inputs.exec]]
+  ## Commands array
+  commands = ["/tmp/test.sh", "/usr/bin/mycollector --foo=bar"]
+
+  ## measurement name suffix (for separating different commands)
+  name_suffix = "_mycollector"
+
+  ## Data format to consume.
+  ## Each data format has its own unique set of configuration options, read
+  ## more about them here:
+  ## https://github.com/influxdata/telegraf/blob/master/docs/DATA_FORMATS_INPUT.md
+  data_format = "json_v2"
+```
+
+{{< telegraf/data-formats type="input" >}}

content/telegraf/v1/output-data-formats/_index.md

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+---
+title: Telegraf output data formats
+list_title: Output data formats
+description: Telegraf serializes metrics into output data formats.
+menu:
+  telegraf_v1_ref:
+    name: Output data formats
+    parent: data_formats_reference
+    identifier: output_data_formats_reference
+    weight: 20
+tags: [output-data-formats, output-serializers]
+
+Telegraf supports the following output data formats for serializing metrics.
+Output plugins that support these formats include a `data_format` configuration option.
+
+For example, in the [File output plugin](/telegraf/v1/output-plugins/file/):
+
+```toml
+[[outputs.file]]
+  ## Files to write to, "stdout" is a specially handled file.
+  files = ["stdout"]
+
+  ## Data format to output.
+  ## Each data format has its own unique set of configuration options, read
+  ## more about them here:
+  ## https://github.com/influxdata/telegraf/blob/master/docs/DATA_FORMATS_OUTPUT.md
+  data_format = "influx"
+```
+
+{{< telegraf/data-formats type="output" >}}